US crude oil futures closed Friday's session down 48 cents at $59.15 per barrel after weekly data from oilfield services firm Baker Hughes showed U.S. drillers continued to draw down the number of rigs exploring for oil.
The oil rig count fell by 24 to a total of 679, down from 1,527 at the same time last year. The report marked the 21st consecutive week that energy firms took more rigs offline than they added.
Brent was down 37 cents at $66.42 a barrel by 2:38 p.m. EDT (1438 GMT). It rose to a 2015-peak of $66.93 on Thursday and increased 21 percent in April. West Texas Intermediate traded as high as $59.90 a barrel before settling.
Oil prices eased off 2015 highs on Friday as the dollar strengthened and after Iraq said its crude oil exports hit a record in April.
Brent and U.S. crude rallied between 20 and 25 percent in April, helped by a weaker dollar and bets that a global supply glut would ease, following the June-to-January sell-off that halved prices from above $100 a barrel.
News that Iraq's oil exports rose in April to a record 3.08 million barrels per day from 2.98 million bpd in March served as a reminder of ample supply in the market.
Iraq's data highlights increasing output from OPEC members, whose supply in April rose to its highest in more than two years at 31.04 million bpd, according to a Reuters survey.